A great deal of effort has heretofore been made for attaining higher sensitivity of silver halide photographic light-sensitive materials. In a silver halide photographic emulsion, a sensitizing dye adsorbed to the surface of a silver halide grain absorbs light entered into a light-sensitive material and transmits the light energy to the silver halide grain, whereby light sensitivity can be obtained. Accordingly, in the spectral sensitization of silver halide, it is considered that the light energy transmitted to silver halide can be increased by increasing the light absorption factor per the unit grain surface area of a silver halide grain and thereby the spectral sensitivity can be elevated. The light absorption factor on the surface of a silver halide grain may be improved by increasing the amount of a spectral sensitizing dye adsorbed per the unit grain surface area.
However, the amount of a sensitizing dye adsorbed to the surface of a silver halide grain is limited and the dye chromophore cannot be adsorbed in excess of the single layer saturation adsorption (namely, one layer adsorption). Therefore, individual silver halide grains currently have a low absorption factor in terms of the quantum of incident light in the spectral sensitization region.
To solve these problems, the following methods have been proposed.
In Photographic Science and Engineering, Vol. 20, No. 3, page 97 (1976), P. B. Gilman, Jr. et al. disclose a technique where a cationic dye is adsorbed as the first layer and an anionic dye is adsorbed as the second layer using the electrostatic force.
In U.S. Pat. No. 3,622,316, G. B. Bird et al. disclose a technique where a plurality of dyes are adsorbed in multiple layers to silver halide and the Forster-type excitation energy transfer is allowed to contribute to the sensitization.
In JP-A-63-138341 (the term “JP-A” as used herein means an “unexamined published Japanese patent publication”) and JP-A-64-84244, Sugimoto et al. disclose a technique of performing the spectral sensitization using the energy transfer from a light-emitting dye.
In Photographic Science and Engineering, Vol. 27, No. 2, page 59 (1983), R. Steiger et al. disclose a technique of performing the spectral sensitization using the energy transfer from a gelatin-substituted cyanine dye.
In JP-A-61-251842, Ikegawa et al. disclose a technique of performing the spectral sensitization using the energy transfer from a cyclodextrin-substituted dye.
With respect to the so-called linked dye having two separate chromophores which are not conjugated but linked by covalent bonding, examples thereof are described in U.S. Pat. Nos. 2,393,351, 2,425,772, 2,518,732, 2,521,944 and 2,592,196 and European Patent 565,083. However, these are not used for the purpose of improving the light absorption factor. In U.S. Pat. Nos. 3,622,317 and 3,976,493 having an object of improving the light absorption factor, G. B. Bird and A. L. Borror et al. disclose a technique where a linking-type sensitizing dye molecule having a plurality of cyanine chromophores is adsorbed to increase the light absorption factor and the energy transfer is allowed to contribute to the sensitization. In JP-A-64-91134, Ukai, Okazaki and Sugimoto disclose a technique of bonding at least one substantially non-adsorptive cyanine, merocyanine or hemicyanine dye containing at least two sulfo and/or carboxyl groups to a spectral sensitizing dye which can be adsorbed to silver halide.
In JP-A-6-57235, L. C. Vishwakarma discloses a method of synthesizing a linked dye by a dehydrating condensation reaction of two dyes. Furthermore, in JP-A-6-27578, it is disclosed that the linked dye of monomethinecyanine and pentamethineoxonol has red sensitivity. However, in this case, the light emission of oxonol and the absorption of cyanine are not overlapped and the spectral sensitization using the Forster-type excitation energy transfer between dyes does not occur, failing in attaining higher sensitization by the light-converging action of linked oxonol.
Furthermore, in EP-A-0985964, EP-A-0985965 and EP-A-0985966, Richard Parton et al. disclose a technique where a combination of a cationic dye and an anionic dye is adsorbed in multiple layers with an attempt to attain high sensitivity using the energy transfer from the dye in the second to the dye in the first layer.
In these methods, however, the degree of adsorption of sensitizing dyes in multiple layers on the surface of a silver halide grain is actually insufficient and neither the light absorption factor per the unit grain surface area of silver halide grain nor the sensitivity can be sufficiently elevated. A technique capable of realizing practically effective multilayer adsorption is demanded.
Particularly, in the case of a color light-sensitive material, the spectral sensitivity must be present in the objective wavelength range. Usually, in the spectral sensitization of a silver halide light-sensitive material, absorption of a sensitizing dye in a monomer state is not used but J-band formed upon adsorption to the surface of a silver halide grain is used. The J-band has sharp absorption shifted to the longer wavelength side than the absorption in the monomer state and therefore, is very useful to have light absorption and spectral sensitivity in the desired wavelength range. Accordingly, even if sensitizing dyes can be adsorbed in multiple layer to the grain surface to increase the light absorption factor, when the dye in the second or upper layer not directly adsorbed to the silver halide grain is adsorbed in the monomer state, a very wide absorption results and this is improper as the spectral sensitivity of an actual light-sensitive material.
Under these circumstances, a technique of allowing sensitizing dyes to be adsorbed in multiple layers on the surface of a silver halide grain to increase the light absorption integrated intensity per the unit grain surface area and at the same time, enabling to limit the absorption and spectral sensitivity to the width of desired color sensitivity region is being demanded.